Hydrolysis of dimethyldichlorosilane has been known as a method for the production of organopolysiloxanes.
For example, a method for hydrolyzing dimethyldichlorosilane in the presence of a stoichiometrically excess amount of water is known as such a hydrolysis method. In general, where hydrolysis is conducted in the presence of an excess of water as in the above method, there are obtained dimethyl cyclopolysiloxane as the main component of the resulting hydrolyzate, and straight-chain, low-molecular-weight dimethyl polysiloxane having silanol groups at both ends as the remainder.
In the above hydrolysis reaction, hydrogen chloride is generated as a by-product, and this hydrogen chloride is recovered in order to react it with methanol to convert it into methyl chloride which is a starting material for the synthesis of dimethyldichlorosilane. Such a method is described in, for example, JP-A-58-69890. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".)
However, since an excess of water is used in the above method, most of the hydrogen chloride generated is necessarily separated in the form of saturated hydrochloric acid. Part of this hydrochloric acid is recycled for use in the hydrolysis, while the remaining part of the aqueous solution of hydrogen chloride is heated to obtain an HCl-H.sub.2 O azeotropic mixture having a contant boiling point and hydrogen chloride.
That is, the conventional hydrolysis method where dimethyldichlorosilane is hydrolyzed using excess water must require a considerable amount of heat energy for the recovery of hydrogen chloride. Further, where the hydrolysis reaction is conducted in the presence of excess water as in the above method, the reaction system must be cooled because a considerable amount of heat is generated due to the exothermic reaction. Thus, this hydrolysis method is greatly disadvantageous from the standpoint of heat energy.
For the purpose of overcoming the above problems, a method in which dimethyldichlorosilane is hydrolyzed using a stoichiometrically equivalent amount of water has been proposed as described in, for example, JP-A-58-126893.
This hydrolysis method, however, is disadvantageous in that the amount of the hydrogen chloride dissolved in the resulting hydrolyzate becomes large, so that the viscosity of the hydrolyzate becomes high. Furthermore, there is another problem that the hydrolysis reaction cannot proceed sufficiently if conducted in a relatively short period of time, leading to low yields and high production costs.